1. Field of the Invention
The present invention relates to a paper feeding apparatus used with a printer, which draws out one sheet of paper at a time from a paper stacked on a tray and supplies one sheet of paper at a time to the printer, and more particularly, to a paper feeding apparatus used with a printer, having a conveying roller to supply a sheet of paper from a pickup roller to a feeding roller, the conveying roller being detachable from a paper feeding route according to a rotation direction of the pickup roller.
2. Description of the Related Art
In general, a paper feeding apparatus to sequentially supply a plurality of sheets of paper is provided in a printer, a copier, and a facsimile.
FIG. 1 is a cross-sectional view illustrating main portions of a conventional paper feeding apparatus for a printer. Referring to FIG. 1, an ink-jet printer 10 includes a paper feeding portion 20, a conveying portion 40, a printing portion 60, and a paper exhausting portion 80.
The paper feeding portion 20 supplies a sheet of paper P to a printer. The paper feeding portion 20 includes a paper feeding cassette 21 movably installed at a lower side of the ink-jet printer 10 so that the paper P to be printed is stacked in the paper feeding cassette 21, and a pickup roller 24 installed at an upper side of the paper feeding cassette 21, so that a sheet of the paper P stacked in the paper feeding cassette 21 is supplied at a time to the printer 10.
A driving unit (not shown) actuates the pickup roller 24 via a gear train 26, causing the pickup roller 24 to consecutively draw out sheets of the paper P. The pickup roller 24 is connected to a support arm 25 and contacts the paper P due to its weight. Also, the outer surface of the pickup roller 24 is surrounded by a friction part 24a having a comparatively large friction coefficient so that the pickup roller 24 easily draws out sheets of the paper P. Preferably, the friction part 24a is formed of rubber.
The conveying portion 40 guides the paper P supplied to the printer 10 by the paper feeding portion 20, to be conveyed to the printing portion 60. For this purpose, the conveying portion 40 includes a conveying roller 41 which conveys the paper P supplied by the paper feeding portion 20, a guide 43 which guides the paper P to be conveyed to the printing portion 60, and a feeding roller 45 which conveys the paper P to the printing portion 60.
The printing portion 60 performs a printing operation onto the conveyed paper P. The printing portion 60 allows a carriage 61, in which an ink cartridge 63 is installed, to perform an alternating rectilinear motion driven by a driving unit (not shown), and the printing portion 60 performs a printing operation onto the paper P via a printhead 65.
The paper exhausting portion 80 includes a paper exhausting roller 81 which withdraws the printed paper P from the printing portion 60 and stacks the paper P on a paper exhausting stand (not shown).
Since the conveying roller is additionally installed between the pickup roller and the feeding roller, the paper feeding apparatus having the above structure is useful when the size of a printing medium is small.
However, when the conveying roller continuously rotates in a paper feeding route as described above, a new problem occurs. That is, if the paper passing the conveying roller meets the feeding roller, one side of the paper contacts the feeding roller, and the other side of the paper is progressed for a predetermined amount of time such that the paper is aligned in front of the feeding roller. In this case, paper curl occurs between the driving conveying roller and the stopped feeding roller. Subsequently, the paper is fed by a rotation force of the feeding roller and the conveying roller, and thereby a printing operation is performed. In general, a feeding force of the feeding roller is greater than an exhausting force of the conveying roller. When the paper is fed to the printing portion in a state where the paper is engaged with the conveying roller, paper curl is maintained at a constant level, and a printing operation is performed in this state. However, at an instant when the paper escapes from the conveying roller which applies a predetermined force to the paper, the force applied to the paper is varied, causing a variation in a feeding rate. As a result, a white background appears on the printed side of the paper, and printing quality is lowered.